Telephone-exchange system



G. S HOFFMAN.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FlLED MAY3I,1917- Patented Mai. 23, 1920.

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GORDON S. HOFFMAN, 01? BUIZlTING-VILLE, CALIFORNIA.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters li'atent.

Patented Ma1a23, 1920.

Application filed May 31,1917. Serial No. 171,961.

To all whom it may concern:

Be it known that I, GORDON S. ITOFFMAN, a citizen of thellnited States,residing at Buntingville, in the county of Lassen and State ofCalifornia, have invented certain new and useful Improvements inTelephone Exchange Systems, of which the following is a specification,reference being had therein. to the accompanying drawing.

My invention relates to telephone ex change systems and especially tobranch toll line systems.

Tn cases where telephone companies 0pcrate toll lines extending throughdistricts which have become somewhat populated but which are remote fromthe central oilice and not sufficiently settled to warrant the buildingof a separate line, and it is desirable to hold the territory in case offuture develop ment, it becomes necessary to connect branch. or branchesto stations along the line. This, however, is subject to thedisadvantage that such branch stations become a hindrance to the use ofthe main line as a long distance toll line, and an annoyance to thecentral o'lliice operator through electrical disturbances in the branchlines which make them noisy, and by their users listening in and ringingin on a busy line.

lit is the object ofmy invention to over come the objection abovementioned by the provision of a control system consisting of acombination and arrangement of circuits and apparatus whereby theconnection of such branch stations with the main line may be controlledby the operator at the central oflice, which system shall be simple,ec0- nomical and effective in operation and may be readily installed atlow expense compared to that of making an additional line.

The invention consists geiieraliy in the provision ofclectromagnetically operated switching means associated with each branchline operable to control the connection between the branch and the mainline, and itself controlled preferably from the central station or fromboth ends of the main line and one or more of the branch stations, thecontrol being el'lected over a grounded circuit phantomed on the mainline throughone winding of repeating coils, through which the talkingcircuits are connected to the main line.

The invention further consists in the various combinations andarrangements of apparatus and circuits as described and illus trated inthe accompanying specification and drawings and particularly pointed outin the appended claims.

My invention is illustrated in the accompanying drawings in which-Figure 1 is a diagrammatic view of a preferred form of my invention. I

Fig. 2 is a similar view showing a method of controlling the branch lineconnections from a branch station.

Fig. 3 shows an arrangement for efiecting; the central oflice controlthrough contacts in the terminal jacks of the main line.

Fig. t shows an arrangement for controlling a branch line connectionindividually.

Referring; to the drawings in detail, the circuits and apparatusindicated to the left of the vertical dotted line in Fig. 1 consti tutethe Central o'llice line terminal ar angement of my invention. Thisportion. of the system consists of a repeating coil 1 having its primarywinding 2 bridged across the terminals of the main trunk line conductors3-4, and its secondary coil 5 bridged across the terminals of a linejack 6, which jack may have multiple connections, not shown, leading toother jacks in a manner well understood by those skilled in the art. Therepeating coil 1 has a central. tap 7 which connects through a suitableconductor 8 and an operators control key 9 to a grounded battery 10. Themain toll line 3i leads out of the central oflice station to one or moredistant exchanges, not shown, as is the usual practice in the use ofsuch lines. At one or more points intermediate the central office andthe distant exchanges, usually, in practice, points more or less remotefrom the central oflice, a branch or branch lines are connected with themain line, as indicated in the dotted rectangles 1]. and 12. Thisconnection is made through a repeating; coil 13,

the primary winding 14- of which is bridged across the main line and isprovided with. a central tap as at 15 connected through a conductor 16and the windings of a relay 17 to round. The secondary winding 18 of therepeating coil 13 has its terminals connected to the branch line 1920through conductors 2122 and norm ally closed contacts 23-24 of the relay17. The primary windings 2 at the central oflice and 1d at the branchline connections are, of course unidirectional coils so that by tappingat the center as at 7 or 15, it forms a differential, winding offeringimpedance to the flow of alternating current across the trunk conductorsand forming a non-inductive resistance for direct current passing inopposite directions through this winding. It will thus be seen that therelay 17 is included with the battery 10 in a grounded phantom circuitwhich may be traced as follows: battery 10, key 9, conductor 8, 7primary winding 2 in opposite directions to trunk conductors 34, primaryWinding let in opposite directions to tap 15, conductor 16, winding ofrelay 17 to ground and back to battery 10.

In the drawings, for the sake of clearness, I have omitted variousdetails and accessories such as signaling, listening, calling andtesting-apparatus which, it is to be understood, could be readily addedby those skilled in the art.

In the use and operation of my invention as illustrated in Fig. 1, theapparatus and circuit connections are normally in condition as indicatedin the diagram, with the operators control key 9 open and the relay orrelays 17, associated with the branch lines, deenergized. This leavesthe branch lines normally connected with the main line through theirrespective repeating coils 13 so that they may signal over the main linewhen it is to be found in idle condition and also receive signals andtalk thereover through suitable substation apparatus connected with thebranch conductors 1920, but not shown. hen it is desired to use the mainline for trunking a long distance call from the central station, thecentral station operator makes the talking connection with the main linethrough the jack 6 in the usual manner and closes the key 9 which clearsthe main line of the branch circuit connections by energizing the relayor relays 17 over the phantom circuit previously described. Thisenergization of the relay 1? causes it to attract'its armature, openingthe contacts 23 and 24 which disconnects the branch line 1920 from'theleads 2122, thus severing operative connection between the branch lineand the main line. The relay 17 is held energized from the centralstation during the use of the main line as a long distance trunk. Thestation or stations on the branch line have no means for controllingthis connection and so cannot interfere with the use of the trunk byringing or listening in; At the end of this use of the trunk, theoperator at the central ofiice may release the relay 17 by opening thekey'9 which relay upon deenergization permits its armature to retractand again.

close the connection from the branch line to the main line through thecontacts 23'24. In practice I use a 500 ohm double contact relay for therelay17, and adjust the battery 10 according to the resistance of theline. It is obvious that in cases where the line 3-4 is to be used as atwo-way trunk, controlling means such as that shown at the centralstation in Fig. 1 may be duplicated at the remote exchange.

In some cases where it is desired to give the branch stations control oftheir connection with the main line, I provide the arrangement as shownin Fig. 2 in which a relay 25 having normally open contacts included inthe connection between the branch line and the main line is substitutedfor the relay 17 of Fig. 1. This relay 25 is arranged to be controlledfrom the branch station by a key 26 situated at the branch station andincluded in the circuit of a local battery 27 connected across theterminals of the relay. With this arrangement the branch line 19-20 isnormally disconnected from the main line 8-4- so that any electricaldisturbances on the branch line will not affect the use of the main lineby the central oilice or other branch stations connected therewith. Aparty at the branch station, however, can

connect with the main line by closing the key 26 which connects theterminals of the local battery across the terminals of the relay 25which upon 'encrgization operates to close the normally open contacts2829 connecting the branch line 19-20 across the terminals of thesecondary winding 18 of the repeating coil 13 and consequently placingthe branch in operative connection with the main line through thesecondary coil 14. When the operator at the central station desires toconnect the branch station with the line for the purpose of calling thesame, she may do so by energizing the relay 25 over a circuit such asthat previously described for Fig. 1.

In order to make the control of the branch line relay or relays 25automatic upon the insertion of a plug in the line jack at the centralstation, I provide the arrangement as shown in Fig. 3 which is in allrespects similar to the line terminal arrangement of Fig. 1 except thatthe conductor 8 connects with the battery 10 through normally opencontact springs 30 arranged to be closed upon the insertion of a plug inthe jack 6.

In order to enable a subscriber at a branch station having the circuitarrangement of Fig. 2 to energize his control relay 25 withoutenergizing those of any other branch. stations that might be connectedto the same main line, I connect the relay 25 as shown in Fig. 4c, thecircuit arrangement remaining the same as that of Fig. 2 except that theenergization of the relay .25 of the branch station is controlled by amake-and-break contact key 31 arranged to keep the relay 25 normallyconnected with the conductor 16 through the normally closed contact 32and upon operation to disconnect the relay from the conductor 16 andconnect it to the free side of the grounded battery 27 through thenormally open contact It will be seen that with this arrangement therelay 25 is normally connected for energization from the central otliceover the phantom circuit and upon actuation of the key 31 will beenergized by current from the battery ii? in a local circuit entirelydisconnected from the main line. Thus the central otlice operator isgiven control of the relays of all the branch stations while each branchstation has control only of its individual relay so that the main linewhen connected with it will be free of all other branch connections.With several branch stations on the main line having relays 25 connectedas shown in Fig. t, a branch station could not :all the other branchstations but could call the central station from which the relays 25 theother branch stations could be Operated to complete a connection betweensuch stations, thus permitting connection between branch stations, butunder supervision of the central station.

My invention may be applied to the control over a two-wire talkingtrunk, or the connection of a central othce with a toll line for talkingthereover to either end of the toll line to the exclusion of the other.

While I have herein shown and described certain preferred forms of myinvention, it is to be understood that various other modifications maybe made thereof without departing from the spirit of the invention andthat all such modifications are contemplated by me. For example, it willbe obvious to those skilled in the art that the circuit conductorsconnected to the central. Oll'lCG 210k and control key may be connectedinstead to the contacts of automatic switching mecha nism tor use inautomatic exchange systems. Again it will be obvious that where thebranch line control arrangement of Fig. 41: is

sed and installed near the telephone set at the branch station, thebattery 27 may be done away with and the branch line connectioncontrolled manually at the central otlice in any well known manner.However, it is usual and preferable to install the apparatus, associatedwith the branch line, at or near the junction with the main line.

llavin g thus described my invention what I claim and desire to secureby Letters Pat- 1. In a telephone exchange system, a toll line, a branchline, a repeating coil connecting said lines intermediate the terminalstations 011 the toll line, and an electrically operated switching meansin said branch circuit energized in a simplex circuit phantomed on thetoll line through a winding of the repeating coil, and controlling meansat the central oflice for said simple): circuit.

2. In a telephone exchange system, a toll line, a branch line, arepeating coil having one winding bridged across the toll lineintermediate the terminal stations on the toll line, and the otherwinding connected to a branch line, an electrically operated switchingmeans having contacts included in the branch line and itself connectedbetween a central point of the said bridged winding and ground, arepeating coil at the central station having one winding bridged acrossthe toll line, and means at the central station for connecting a sourceof current between a central point of the said the central station andground.

8. In a telephone exchange system, a toll line, a branch line, arepeating coil connecting said lines intermediate the terminal stationson the toll line, electrically operated switching means in said branchline, a simplex energizing circuit for said switching means including asource of current and phantomed 011 the toll line through one winding ofsaid repeating coil, and controlling means for said energizing circuit.

t. In a telephone exchange system, a toll line, a branch line, arepeating coil connecting said lines intermediate the terminal stationson the toll line, electrically operated switching means in said branchline, means at the central station for controlling said switching means,and other means associated with said branch circuit for controlling saidswitching means.

5. In a telephone exchange system, a toll line, a plurality of branchstations intermediate the terminal stations on the toll line,electromagnetic switching means at each branch station for connectingits associated station with said toll line, said electromagnetic meansbeing connected in multiple in a simplex circuit phantomed on the tollline, a local source of energy at each of said terminal and. branchstations, and means at each said station for connecting its localsoiu-ce oi energy across said simplex circuit in multiple with saidelectromagnetic means.

In testimony whereof I aflix my signature.

GORDON S. HOFFMAN.

bridged winding at

